SageModeler is a free online simulation tool designed for diagramming and modeling dynamic interactions among components of a system. Users lay out the components of a system, set their initial conditions, and define their interactions. Strength of interactions can be controlled with “valves”. Connections are unlabelled. The simulation can then model how changing levels of one component affect the rest of the system, and can model time-dependent behaviour. Model results can be shown in various ways, such as simple graphs of component levels. The tool can be used at various levels of detail and complexity.
System components are necessarily limited to those where an “increase” or “decrease” is meaningful, but that still allows modeling of a wide range of systems; examples given on the SageModeler website include chemistry, biology, physics, epidemiology, and more.